The objective is to study the effects of prostaglandin E2 (PGE2), a naturally occurring substance and a known modulator of erythropoiesis, on rat erythroid cell hemoglobin (Hb) proportions. The rat has no specifically fetal Hb, in contrast to humans. However, rats and humans share a number of similarities in Hb switching during ontogeny and differentiation. Postnatal changes in proportions of beta-like chains, and asynchronus synthesis of these chains during maturation of adult erythroid cells, are seen in both species. Erythropoietic stress in man leads to fetal Hb synthesis in adult life. Likewise, rat Hbs show partial reversion toward newborn Hb proportions upon anemic stress. In humans, genetic variation near the beta chain locus can lead to high F-reticulocyte levels. Similarly, two rat Hb genotypes AA and BB are known, which differ in both structure and proportions of certain Hb components. These similarities between rats and humans stimulate this short proposal with a long-term objective which aims at establishing rat as an experimental animal for manipulating Hb components at will in adult life, avoiding adverse side effects. This project will study: I. For rat genotype AA and BB, the total Hb synthesis of cultured cells from adult marrow in response to PGE2, hydroxyurea and 5-azacytidine and to compare their influence on the concurrent DNA synthesis. II. The respective effect of injecting these agents into anemic adult rats and to separate Hb components by DEAE-cellulose chromatography and globin chains by carboxymethyl cellulose chromatography, in order to account for any differences in Hb proportions. III. The effects of anemia per se on plasma PGE2 level. The data to be obtained will indicate the possible involvement of factors in the control of relative synthesis of Hb components, and will define the role of PGE2 in this process. Knowledge of control mechanisms affecting the proportions of major and minor Hbs in rats should be useful in designing future treatments for diseases such as sickle cell anemia and thalassemia.